In radiotelephone systems such as the Global System for Mobile Communications (GSM) radiotelephone system in use in Europe, a SIM card is inserted into a radiotelephone for providing subscriber identification, billing information and other information concerning the operation of the radiotelephone. The SIM is a key component of the GSM and typically comprises a smart card which is inserted into a GSM phone in order to make the phone work.
In a typical cellular telephone communication system, each subscriber unit is assigned a mobile subscriber (MSI) which uniquely identifies the subscriber unit from other subscriber units. In the European cellular communication system, one such identifier is the international mobile subscriber identification number (IMSI).
It is highly desirable to provide a personal communication system which has a single personal telecommunications device which is operable in all available cellular systems, e.g., AMPS, TDMA, CDMA, GSM, etc. across all available cellular frequencies, e.g., 900 MHz or 1800 MHz as well as satellite frequencies, and which operates like an inexpensive cordless phone when the user is at home.
In conjunction with such an approach the user has a single phone number, and that phone number tracks that phone such that wherever the phone is, that is where the user is. In those approaches each universal identification number or telephone number may have multiple network numbers associated with it to permit the single telephone number to be used in different networks.
In the SIM environment, a user is not constrained to carry his own personal communications device on him at all times, since it is SIM plus a generic, non-user specific communications device which the system sees, as opposed to a specialized, user specific device such as a conventional wireline phone or a conventional non-GSM cellular phone. In a network where you have one user-one number, this is desirable.
It may be desirable for a person to have two universal numbers, one for personal communications, and one for work. It seems unlikely that it would be desirable to have a single number used for both work and a personal life, as these two different types of calls usually require different telephone mannerisms when first answering such calls. In such dual number cases, the personal number may be in force almost all the time, while the work number is used primarily at the office but occasionally at home or while in the car. In such case, it would be desirable for the user to be able to receive calls in secure communications mode for both numbers.
In another situation easiest understood by way of an example, a computer network person assigned to a help line may be on call for overnight or weekend emergency service. If the computer help line numbers is on a SIM, a computer network specialist could take that SIM home and place it in his home telephone coupled to the conventional wire line phone and receive help line calls there or in his car phone while driving around town, both using a secure mode of communications. However, at the same time he would like to be able to receive personal calls from his personal number.